Solidified plastic matrix containing white phosphorous



nited States ABSTRACT OF THE DISCLOSURE A plastic matrix containing White phosphorous for use at elevated temperatures as the smoke generating contents of an artillery marking shell.

A process wherein finely divided particles of white phosphorous are encapsulated within a plastic or resinous binder by mixing, and which may include the reduction of bulk forms of white phosphorous to a fine powder coupled with a desensitization of the particles of white phosphorous with copper sulfate.

This invention relates to an improved smoke generating composition for use at elevated temperatures in an artillery shell. More particularly, this invention relates to a smoke generating composition consisting of white phosphorous encapsulated Within a solidified plastic or resinous matrix.

Artillery shells containing white phosphorous are generally utilized for marking ranges and targets. Upon impact, the shell will burst and the white phosphorous will be spread in the air, in the form of an umbrella. Upon exposure to the air, the white phosphorous will burst into flames and give off a tremendous amount of white smoke which can be visually sighted for accuracy and adjustment of fire power.

However, in the past, artillery shells containing white phosphorous were found to be highly erratic with respect to their flight characteristics and, as a result, grossly unreliable in the absolute requirement for accuracy if stored for any appreciable length of time, prior to firing, in a relatively hot environment such as that encountered in Southeast Asia. As a result, the forward observers who were entrusted with the duty of calculating range for our heav-y guns were finding it difficult, if not impossible, to carry out their function properly. One of the factors, which has effected the use of white phosphorous in artillery shells at elevated temperatures, is the comparatively low melting point, approximately 44 C., of the white phosphorous itself. When the rounds are subject to storage in an environment in which the temperature exceeds 44 C., the solidified mass tends to liquefy and, as a fluid, is then responsive to forces causing movement within the shell which affects the ballistic stability and ultimately the accuracy of the round involved.

Therefore, the munition art recognized that to have a consistently reproducible trajectory and a greater degree of accuracy, it is necessary to prevent movement of the payload within the shell during flight.

With this view in mind, attempts were made to overcome the disadvantages of the art and to give flight stability to shells containing white phosphorous. For instance, porous aluminum sponges were utilized to prevent the overall movement of the liquefied white phosphorous within the shell by absorbing the fluid. However, although the sponges prevented a major movement of the liquefied mass, the sum total of the incremental movement of the various portions of the fluid still tended towards flight instability and ultimate inaccuracy of the round.

Patented Mar. 4, 1969 Another attempt was to add numerous high melting ingredients to the White phosphorous in order to prevent its liquefication at elevated temperatures. However, of all materials tested, it was found that, when sufficient additives were added to prevent liquefication, the primary function of the white phosphorous as a marker was adversely affected. When the amount of additives was reduced so that the white phosphorous could accomplish its primary function, the melting point of the white phosphorous was hardly affected and the solidified mass would again be transformed into a liquid at the ordinary temperatures encountered in areas such as Southeast Asia, and the like.

A further attempt was made to convert a portion of the white phosphorous to red phosphorous on exposure to air or by a slight burning of the outer surface of the white phosphorous. As is well known, red phosphorous is not as readily subjected to oxidation upon exposure to air and also requires ground glass, as a friction producing agent, or an oxidizer to ignite it. However, this approach was not at all welcomed as a procedure for use in industrial production because it was highly diflicult to accomplish and hazardous.

The aforesaid disadvantages of the art are substantially overcome by the present invention, hereinafter described, with particular reference to the use of white phosphorous in artillery shells at elevated temperatures. However, it is to be understood that the use of the present invention is not limited to artillery shells, but that the invention has numerous advantages when employed in a use which requires prior storage at elevated temperatures.

It is, therefore, an object of this invention to provide a composition, which is essentially white phosphorous, for use as a smoke generating medium in artillery shells which are to be exposed to the ordinary temperatures encountered in areas such as Southeast Asia and the like.

Another object is to prevent flight instability in artillery shells containing white phosphorous by modifying the composition itself.

A further object is to provide a novel form of white phosphorous for use in artillery shells and a process of making the same.

We have now discovered a means whereby white phosphorous may be utilized in an artillery shell, at elevated temperatures, without adversely affecting the flight characteristics or the accuracy of the shell. This discovery lies in the encapsulating of discrete particles or aggregates of particles within a solidified plastic shell or resinous matrix. Artillery shells of the 40 mm. variety containing white phosphorous encapsulated in the manner described have demonstrated reproducible flight stability and consistent accuracy over the full, 1600 yard, range at Aberdeen Proving Grounds, Md. The shells, which were fired, were all preconditioned by being stored for 24 hours at temperatures in the range of F. prior to use. However, the latter treatment did not adversely effect the flight or accuracy of any of the artillery rounds which were fired.

The discrete particles or small aggregates of particles of white phosphorous may be encapsulated within a matrix formed by any of the following plastic materials, definitions of all of which may be found in the Military Standardization Handbook titled Plastics, MilHDBK 700(MR), dated Nov. 1, 1965, viz: polyesters, epoxides, and silicones.

In addition, the following classes of resinous or plastic-like materials may also be utilized to advantage either alone, or in combination, to form the thin plastic matrix within which the small, discrete, particular like aggregates of white phosphorous are encapsulated. These include polyamides, phenolic resins, polysulfones, formaldehyde resins, thiokols, polythioethers and silicones.

Further, plastic-like lacquer films of explosive materials such as nitrocellulose may also be utilized to advantage as the encapsulating medium.

The following examples, i.e. I and II, illustrate the process of encapsulating white phosphorous, which is an extremely hazardous material, within a thin plastic or resinous matrix.

Example I Particles of white phosphorus of the size desired, which are thoroughly wet with water, are washed with acetone which is a water miscible solvent. At least three washes with such solvent are recommended. After each wash, the solvent is decanted. The particles of white phosphorous, which are now wet with solvent, are placed in a mixing kettle and a flow of inert gas such as nitrogen is mamtained over the surface of the particles. Agitation is commenced and when the particles of white phosphorous are dry and free-flowing, the liquid plastic material is added of the kettle. When the particles of white phosphorous and plastic liquid are thoroughly mixed, the flow of inert gas is discontinued. If a catalyst is required, it may now be added to the mass and agitation continued. The encapsulated white phosphorous is now ready for loading into shells or molds. The mixture is then either poured or extruded into the required end item and cured overnight at ambient temperature or a slight amount of heat may he applied to the mass to accelerate cure time.

Example 11 100 gms. of white phosphorous having a particle size between and 1000 microns are placed in a sigma-blade provided mixing kettle and gms. of a liquefied plastic are added thereto. It is to be noted that at this time the white phosphorous is covered by a thin layer or blanket of water. The materials are agitated until the particles of white phosphorous and the liquid plastic are thoroughly mixed at which time the excess water is decanted. It has been found that excess water will rise to the surface under a slight amount of pressure. This excess water is decanted and the sample allowed to effect an insitu polymerization. Large exposed surface areas of white phosphorous may be then treated with an appropriate silicate to reduce chance of incidence. However, if a catalyst is required, it is now added to the mixing kettle and agitation continued until the catalyst is thoroughly disposed throughout the mass. The mass of encapsulated white phosphorous may now be extruded or manually placed into the molds or shell by means of a spatula-like tool.

The amount of plastic or resinous material utilized in the process should be in the range of between about 10 and 50 percent 'by weight. If an amount below 10 percent is utilized, it has been found that there will not be enough plastic or resinous material to completely encapsulate the individual or small, discrete aggregates of white phosphorous. If an amount above about 50 percent is utilized, the product will not function properly and will produce less than the required amount of flame and smoke. The preferred amount of plastic material, for use in the processes set forth in Examples I and II, is about 25 percent. It has been found that in this specific range a strong product is produced and an optimum amount of smoke or flame is obtained upon burst.

The white phosphorus should have an average particle size between about 50 to 1,000 microns. If the average size of the particles is substantially greater than 1,000 microns, the material is notably less stable. The preferred average range is between 200 to 500 microns due to the fact that a maximum amount of smoke is produced per specific weight of the white phosphorous within this range. Further, the burning characteristics of the white phosphorous may be varied by varying the size of the particles. Therefore, control of particle size is essential, when short or prolonged burning rates are desired.

The following examples, i.e. III to IV, will illustrate the methods utilized to form and maintain the desired size of the particle of white phosphorous prior to processing.

Example III A beaker containing 30 gms. of white phosphorous under a blanket of 400 mls. of water was placed in a water bath and the temperature of the system was raised to 60 C. When the solidified mass was completely liquefied, the beaker was removed from the water bath and fitted with two side baffles. It is to be noted that to assist in particle refinement, bafiie plates can be added for increased turbulency. A propeller-blade type agitator was placed in the beaker, the blades being 0.25 inch from the bottom of the beaker. When the temperature of the liquefied mass dropped to about 53 C., agitation was started and maintained at 450 revolutions per minute for a period of 4 to 5 minutes. In this manner, liquid white phosphorous was thoroughly dispersed throughout the slurry. It has been found that the speed of the mixer may be correlated to the particle size desired. At this time, 350 mls. of water having a temperature of 5 C. was added to the beaker to resolidify the white phosphorous into a multitude of discrete finely divided particles. The agitator was then stopped, at which time, the agitator and the baffles were removed from the system. The excess water was removed from the beaker, but a wet blanket of water was allowed to remain over the discrete, solidified particles of white phosphorous. The particles of white phosphorous were then screened and particles in the range of 50 to 1,000 microns were collected for processing in accordance with the procedure set forth in Examples I and II.

Example IV 10 gms. of white phosphorous in the bulk form was dissolved in carbon disulfide and slowly added to either ethyl acetate or acetone which is under rapid agitation. Very fine particles of white phosphorous were precipitated from the solvent media. The solvents were then decanted therefrom and then the particles of white phosphorous were washed several times with water.

Example V White phosphorous in the bulk form, under water, was ground by a mechanical grinder. The finely divided particles of white phosphorous were then transferred to a sieve where the undesired portion was removed.

Example VI White phosphorous was liquefied under water at 60 C. The melt was then fed by regulatory valve into agitated water whose temperature was below 30 C. It was found that droplet size might be regulated by varying the orifice diameter of the nozzle. Also, an inert blanket of nitrogen may be maintained over the surface of the agitated water.

In order to partially desensitize the particles of white phosphorous for a relatively short time so that they will not immediately burn in air and to allow processing, the particles are treated with copper sulfate solution. This has been found to insure, for a short time, the integrity of the discrete particles even though they may later melt. This may be accomplished by slurrying the particles in a 5 percent aqueous solution of copper sulfate for 5 minutes, at which time, the excess sulfate solution is removed by decantation and washing. The acidic water formed by the reaction is removed, and the coated particles are washed in acetone. Finally, these particles are dried under an inert blanket of nitrogen prior to encapsulation. It has been found that small uniform particles of white phosphorous are formed. It is believed that the copper coating produced, as described above, enhances the bond of the resinous or plastic material to the particles of white phosphorous thereby increasing the strength of adhesion of the encapsulating matrix to the particles.

Not only does the encapsulating of white phosphorous with a plastic or resinous matrix solve the problem of flight instability and inaccuracy of shells containing white phosphorous, but also it has been found that there are many attendant advantages which are gained by this technique. These include the fact that the binder case bonds to the metal hardware of the interior of the shell to prevent movement, so that set back forces high rates of acceleration and rotational forces may be withstood. One may control the size of the particle of white phosphorous and concentration of resinous binder and, in this way, control the burning rate of the white phosphorous. Safety is achieved in atmospheric shell loading and large batches may be easily prepared for larger weapons. Simplicity is achieved with ease of manufacture by the cast technique and the cost of manufacture is small.

Obviously, many modifications and variations of the present invention will become apparent to one skilled in the art in view of the above teaching. For instance, this system may be used in the production of other pourable high energy items. A system consisting of magnesium, potassium, or sodium nitrate and related compounds used in pyrotechnics can be easily encapsulated by this binder system and made into a poura-ble mix and thereby, simplifying the pyrotechnic method of production. It is therefore to be understood that this invention, as set forth in the appended claims, may be practiced otherwise than as specifically described.

We claim:

1. White phosphorous encapsulated within a solidified plastic matrix selected from the group consisting of polyester resin, epoxide resin, silicone resin and nitrocellulose, said phosphorous being for use in artillery shells at elevated temperatures.

2. The product of claim 1 wherein said matrix is composed of at least one polyester resin.

3. The product of claim 1 wherein said matrix is composed of at least one epoxide resin.

4. The product of claim 1 wherein said matrix is composed of at least one silicone resin.

5. The product of claim 1 wherein said matrix is composed of a nitrocellulose lacquer.

6. The product of claim 1 wherein said matrix represents between about 10 and about percent by weight of said encapsulated white phosphorous.

7. The product of claim 6 wherein said matrix is composed of a polyester resin.

8. The product of claim 6 wherein said matrix is composed of an epoxide resin.

9. The product of claim 6 wherein said matrix is composed of a silicone resin.

10. The product of claim 6 wherein said matrix is composed of a nitrocellulose lacquer.

11. A process of encapsulating particles of white phosphorous in a solidified plastic matrix selected from the group consisting of polyester, epoxide, silicone and nitrocellulose comprising coating said white phosphorous with copper sulfate to desensitize the white phosphorous and subsequently, mixing said coated white phosphorous under a blanket of water with said plastic in fluid form.

References Cited UNITED STATES PATENTS 2,574,466 11/1951 Clay et a1. 149-29' X 2,658,874 11/1953 Clay et a1. 14929 X CARL D. QUARFORTH, Primary Examiner.

S. J. LECHERT, Assistant Examiner.

U.S. Cl. X.R. l4920, 29, 96 

